Image sensor and stacked structure thereof

ABSTRACT

There are provided an image sensor and a stacked structure thereof. The image sensor includes a pixel array in which a plurality of unit pixels for generating an output signal in accordance with incident light are arranged, a first amplifier having a first input dynamic range, and a second amplifier having a second input dynamic range that is larger than the first input dynamic range. One of the first and second amplifiers amplifies the output signal in accordance with the intensity of light.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C §119, of KoreanPatent Application No. 10-2014-0057444, filed on May 13, 2014, in theKorean Intellectual Property Office, the contents of which isincorporated herein in its entirety by reference.

FIELD OF INVENTION

The inventive concept relates to an image sensor and a stacked structurethereof, and more particularly, to an image sensor including a pixelarray and a stacked structure thereof. The inventive method may furtherrelate to a method of making, implementing, and using same, as well asmethods of its operation.

BACKGROUND

Image sensors used to photograph subjects and convert the photographedimages into electrical signals are used in cameras mounted on a vehicle,a security apparatus, and a robot, as well as in general consumerelectronics, such as a digital camera, a mobile phone camera, and aportable camcorder. Such an image sensor may include a pixel array andunit pixels included in the pixel array may respectively include photodetecting devices. The photo detecting devices may generate electricalsignals in accordance with the intensities of absorbed light. Forexample, among the photo detecting devices, photodiodes may absorb thelight to generate currents.

An image sensor may include transistors for controlling photo detectingdevices, a circuit for driving a pixel array, and a circuit formeasuring output signals of the pixel array as well as the photodetecting devices. The photo detecting devices, the transistors forcontrolling photo detecting devices, the circuit for driving a pixelarray, and the circuit for measuring output signals of the pixel arraymay be respectively formed by semiconductor manufacturing processes. Forexample, the electrical signals generated by the photo detecting devicesmay pass through at least one transistor to be converted into outputsignals whose voltages change in accordance with the intensities of theabsorbed light and the pixel array may output the output signalsexternal to another circuit or device.

SUMMARY

In accordance with aspects of the inventive concept, an image sensor isprovided that includes a pixel array that generates output signals inaccordance with incident light and a stacked structure thereof. Theimage sensor may include an amplifier circuit having at least twoamplifiers having different dynamic ranges.

According to an aspect of the inventive concept, there is provided animage sensor including a pixel array having a plurality of unit pixelsconfigured to generate an output signal in response to incident light, afirst amplifier having a first input dynamic range, and a secondamplifier having a second input dynamic range that is larger than thefirst input dynamic range. One of the first and second amplifiersamplifies the output signal in accordance with the intensity of light.

In various embodiments, the image sensor may further include a referencesignal generator configured to generate a reference signal. The firstand second amplifiers may be differential amplifiers configured to eachreceive the reference signal and the output signal as inputs and tomeasure the output signal relative to the reference signal.

In various embodiments, the second amplifier may be a complementarymetal-oxide-semiconductor (CMOS) input folded cascade amplifier.

In various embodiments, the image sensor may include stacked first andsecond chips. The pixel array may be arranged in the first chip. Thefirst and second amplifiers may be arranged in the second chip.

In various embodiments, a feature size of the first chip may be largerthan that of the second chip.

In various embodiments, a power supply voltage of the first chip may behigher than that of the second chip.

In various embodiments, the image sensor may further include at leastone interconnecting member coupled between the first chip and the secondchip to transfer the output signal between the first and second chips.The interconnecting member may be electrically connected to unit pixelscorresponding to a column of the pixel array.

In various embodiments, the image sensor may further include a counterconfigured to convert a signal amplified by the first or secondamplifier into a digital signal. The counter may be arranged in thesecond chip.

In various embodiments, the first and second amplifiers may beconfigured to receive a control signal. A power consumption of the firstamplifier or the second amplifier may be stopped depending on a voltagelevel of the control signal.

According to another aspect of the inventive concept, there is providedan image sensor including a first chip having a pixel array comprising aplurality of unit pixels configured to generate an output signal inaccordance with incident light, a second chip including first and secondamplifiers with different input dynamic ranges, such that one of thefirst and second amplifiers amplifies the output signal depending on theintensity of the incident light, and an interconnecting member arrangedto transmit the output signal from the first chip to the second chip.The first and second chips may be stacked, one at least partially on theother.

In various embodiments, the feature size of the first chip may be largerthan that of the second chip. A power supply voltage of the first chipmay be higher than that of the second chip.

In various embodiments, an input dynamic range of the second amplifiermay be larger than that of the first amplifier. A gain of the firstamplifier may be larger than that of the second amplifier.

In various embodiments, the second chip may further include a referencesignal generator configured to generate a reference signal used tomeasure the output signal. The first and second amplifiers may bedifferential amplifiers that receive the reference signal and the outputsignal as inputs.

In various embodiments, the first and second amplifiers may receive acontrol signal. Power consumption of one of the first and secondamplifiers may be stopped in accordance with the control signal.

In various embodiments, the interconnecting member may be electricallyconnected to unit pixels corresponding to a column of the pixel array.

In accordance with another aspect of the inventive concept, provided isan image sensor, comprising a pixel array comprising a plurality of unitpixels configured to generate a plurality of output signals is responseto incident light; and a plurality of amplifier circuits configured toreceive the plurality of output signals. Each amplifier circuitcomprises a first amplifier having a first input dynamic range andconfigured to amplify the output signal when the incident light has alow intensity and a second amplifier having a second input dynamic rangethat is larger than the first input dynamic range, and configured toamplify the output signal when the incident light has a high intensity.

In various embodiments, the first amplifier may have a larger gain thanthe second amplifier.

In various embodiments, the first and second amplifiers may beconfigured to receive a control signal and a power consumption of thefirst amplifier or the second amplifier may be stopped depending on avoltage level of the control signal.

In various embodiments, the pixel array may be formed on a first chipand the plurality of amplifiers may be formed on at least one secondchip.

In various embodiments, the image sensor may further comprise aninterconnecting member arranged to transmit the output signal from thefirst chip to the at least one second chip, wherein the first chip andthe at least one second chip are stacked.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of one or more new and useful process, machine,manufacture, and/or improvement thereof, in accordance with theinventive concept, are provided in the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view illustrating an embodiment of an imagesensor, according to aspects of the inventive concept;

FIG. 2 is a circuit diagram of an embodiment of a unit pixel, accordingto aspects of the inventive concept;

FIG. 3 is a view illustrating an embodiment of an operation of the unitpixel, according to aspects of the inventive concept;

FIG. 4 is a schematic view illustrating an embodiment of an imagesensor, according to aspects of the inventive concept;

FIG. 5 is a view illustrating an embodiment of an operation of the imagesensor, according to aspects of the inventive concept;

FIG. 6 is a circuit diagram of an embodiment of a first amplifier ofFIG. 4, according to aspects of the inventive concept;

FIGS. 7A and 7B are circuit diagrams of embodiments of a secondamplifier of FIG. 4, according to aspects of the inventive concept;

FIGS. 8A and 8B are circuit diagrams of embodiments of an amplifiercircuit of FIG. 4, according to aspects of the inventive concept;

FIG. 9 is a view illustrating an embodiment of a structure of an imagesensor, according to aspects of the inventive concept;

FIG. 10 is a view illustrating an embodiment of a system including animage sensor, according to aspects of the inventive concept; and

FIG. 11 is a view illustrating an embodiment of an electronic systemincluding an image sensor and interfaces, according to aspects of theinventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Aspects of the inventive concept will now be described more fully withreference to the accompanying drawings, in which exemplary embodimentsare shown. The inventive concept may, however, be embodied in manydifferent forms and should not be construed as limited to the exemplaryembodiments set forth herein.

It will be understood that, although the terms first, second, etc. arebe used herein to describe various elements, these elements should notbe limited by these terms. These terms are used to distinguish oneelement from another, but not to imply a required sequence of elements.For example, a first element can be termed a second element, and,similarly, a second element can be termed a first element, withoutdeparting from the scope of the present invention. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element is referred to as being “on”or “connected” or “coupled” to another element, it can be directly on orconnected or coupled to the other element or intervening elements can bepresent. In contrast, when an element is referred to as being “directlyon” or “directly connected” or “directly coupled” to another element,there are no intervening elements present. Other words used to describethe relationship between elements should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like may be used to describe an element and/or feature'srelationship to another element(s) and/or feature(s) as, for example,illustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use and/or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” and/or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.The device may be otherwise oriented (e.g., rotated 90 degrees or atother orientations) and the spatially relative descriptors used hereininterpreted accordingly.

To the extent that functional features, operations, and/or steps aredescribed herein, or otherwise understood to be included within variousembodiments of the inventive concept, such functional features,operations, and/or steps can be embodied in functional blocks, units,modules, operations and/or methods. And to the extent that suchfunctional blocks, units, modules, operations and/or methods includecomputer program code, such computer program code can be stored in acomputer readable medium, e.g., such as non-transitory memory and media,that is executable by at least one computer processor.

FIG. 1 is a schematic view illustrating an embodiment of an image sensor5 according to aspects of the inventive concept. As illustrated in FIG.1, the image sensor 5 may include a pixel array 1000 and one or moreamplifier circuits 2000. The pixel array 1000 may include unit pixels1100 arranged in one or more columns, such as column 1001. A column maygenerate output signals COL_OUT respectively generated by the unitpixels 1100 of the column, in response to received or incident lightfrom the outside. Other columns of pixels may also output respectiveCOL_OUT output signals, to a respective amplifier circuit. That is, theamplifier circuits 2000 may receive the output signals COL_OUT from thepixel array 1000 and may amplify the received output signals COL_OUT.

According to this embodiment, the unit pixels 1100 included in onecolumn of the pixel array 1000 may share a line used to output thesignals COL_OUT to the outside of or external to the pixel array 1000.For example, as illustrated in FIG. 1, a column 1001 of the pixel array1000 may include six unit pixels and the six unit pixels may share theline used to transmit the output signals COL_OUT respectively generatedby the six unit pixels. In this manner, output signals from all pixelunit light-absorbing components in a column are output to the outside ofthe pixel array 1000 using a shared line. The pixel array 1000 maysequentially select six unit pixels that share one line (that is, sixunit pixels included in one column) and the six unit pixels mayrespectively output the output signals COL_OUT to the outside of thepixel array 1000 with a time difference. Aspects of the unit pixel 1100will be described in detail with reference to FIG. 2.

According to this embodiment, each of the amplifier circuits 2000 mayinclude a first amplifier 2100 and a second amplifier 2200. The firstamplifier 2100 may amplify an output signal COL_OUT to output a firstamplified signal AMP1_OUT, and the second amplifier 2200 may amplify anoutput signal COL_OUT to output a second amplified signal AMP2_OUT. Thefirst amplified signal AMP1_OUT or the second amplified signal AMP2_OUTmay be transmitted to an analog-to-digital converter (ADC) or a digitalcounter and be converted into digital data. In addition, the imagesensor 5 may include a plurality of amplifier circuits 2000corresponding to a plurality of columns of pixels of the pixel array1000. For example, there could be one amplifier circuit for each pixelcolumn. The amplifier circuits 2000 may respectively receive outputsignals COL_OUT from the columns of the pixel array 1000.

Additionally, the first and second amplifiers 2100 and 2200 may berespectively turned on or off in accordance with a control signalCON_SIG. For example, one of the first and second amplifiers 2100 and2200 may stop operating (or consuming power) in accordance with thecontrol signal CON_SIG and the other of the first and second amplifiers2100 and 2200 may operate normally (that is, amplify the output signalCOL_OUT). The control signal CON_SIG may be a signal input to the firstand second amplifiers 2100 and 2200 through at least one line, wherein avoltage level of the control signal CON_SIG may cause one of the firstand second amplifiers to turn off while the other operates.

A range of the intensity of light that may be sensed by the image sensor5 is referred to as a dynamic range of the image sensor 5. If the imagesensor 5 has a large dynamic range, the image sensor 5 may sense animage ranging from a dark image to a bright image. The output signalCOL_OUT generated by the unit pixels 1100 from incident light with lowintensity and output to the outside of the pixel array 1000 may have asmall value (or change amount), and the output signal COL_OUT generatedby the unit pixels 1100 in accordance with light with high intensity andoutput to the outside of the pixel array 1000 may have a large value (orchange amount). For example, the output signal COL_OUT may be anelectrical signal having a voltage that changes in accordance with theintensity of received light and may have a voltage that increases (or isreduced) as the intensity of the light increases.

In order for the image sensor 5 having a large dynamic range to sense adark image, the output signal COL_OUT corresponding to light with lowintensity may be amplified with a large gain. In addition, in order forthe image sensor 5 having a large dynamic range to sense a bright image,the output signal COL_OUT corresponding to light with high intensity mayhave a large value. According to an embodiment, the amplifier circuit2000 may normally amplify the output signal COL_OUT having a largevalue, which may have a larger gain than that of the output signalCOL_OUT having a small value.

According to an embodiment, the first amplifier 2100 may have a firstinput dynamic range and the second amplifier 2200 may have a secondinput dynamic range that is larger than the first input dynamic range.An input dynamic range refers to a voltage range of an input signal thatan amplifier (for example, the first or second amplifier 2100 or 2200)may normally amplify. Therefore, the second amplifier 2200 may have aninput signal range (that is, a range of the output signal COL_OUT thatmay be normally amplified) that is larger than that of the firstamplifier 2100. In addition, according to an embodiment, a gain of thefirst amplifier 2100 may be larger than that of the second amplifier2200. Therefore, the first amplifier 2100 may amplify the output signalCOL_OUT with a larger gain than that of the second amplifier 2200.

According to an embodiment, the first amplifier 2100 may amplify theoutput signal COL_OUT corresponding to the light with low intensity andthe second amplifier 2200 may amplify the output signal COL_OUTcorresponding to the light with high intensity. That is, the firstamplifier 2100 and the second amplifier 2200 may be turned on or off inaccordance with the control signal CON_SIG, which may be controlled inaccordance with the intensity of light incident on the pixel array 1000.For example, the control signal CON_SIG may selectively block a currentpath from a power supply voltage of the first or second amplifier 2100or 2200 to a ground voltage to turn on or off the first or secondamplifier 2100 or 2200.

In this embodiment, the first amplifier 2100 may have a gain larger thanthat of the second amplifier 2200. For example, the first amplifier 2100may have a gain of x3 to x6, while the second amplifier 2200 may have again of x1 to x3. The first amplifier 2100 may generate a firstamplified signal AMP1_OUT by amplifying the output signal COL_OUT havinga relatively small intensity value, which is generated by the unitpixels 1100 of the pixel array 1000 absorbing the light with lowintensity. Therefore, the image sensor 5 may measure the intensity ofthe light with low intensity from the first amplified signal AMP1_OUT,amplified to have a larger value, to improve the resolution of the lightwith low intensity.

In addition, the second amplifier 2200 has the second input dynamicrange that is larger than the first input dynamic range of the firstamplifier 2100. The second amplifier 2200 may normally amplify theoutput signal COL_OUT having a relatively large intensity value, whichis generated by the unit pixels 1100 of the pixel array 1000 absorbingthe light with high intensity, to generate the second amplified signalAMP2_OUT. Therefore, the image sensor 5 measures the intensity of thelight with high intensity through the normally amplified secondamplified signal AMP2_OUT to improve the resolution of the light withhigh intensity.

As illustrated in the embodiment of FIG. 9, in a stacked image sensor5′, unit pixels 1100 of a pixel array 1000 may receive a power supplyvoltage that is higher than that supplied to an amplifier circuit 2000′.Therefore, a range of an output signal COL_OUT output by the pixel array1000 may be large. In particular, the amplifier circuit 2000′ needs tonormally amplify the output signal COL_OUT, such amplificationcorresponding to light with high intensity. Since the second amplifier2200′ has the large second input dynamic range, the output signalCOL_OUT corresponding to the light with high intensity may be normallyamplified.

On the other hand, a line at which the first amplifier 2100′ outputs thefirst amplified signal AMP1_OUT and a line at which the second amplifier2200′ outputs the second amplified signal AMP2_OUT may be electricallyconnected. For example, when the first amplifier 2100′ is turned off andthe second amplifier 2200′ is turned on, in accordance with the controlsignal CON_SIG, the line at which the first amplifier 2100′ outputs thefirst amplified signal AMP1_OUT may be in a high impedance state.Therefore, the second amplified signal AMP2_OUT of the second amplifier2200′ may be normally output without being affected by the firstamplifier 2100′.

FIG. 2 is an embodiment of a circuit diagram of a unit pixel 1100according to an aspect of the inventive concept. The unit pixel 1100 maygenerate an electrical signal corresponding to the incident light itreceives and may output the generated electrical signal externally,outside of the unit pixel 1100 and through column 1001. The unit pixel1100 illustrated in FIG. 2 is only an example, the inventive concept maybe applied to different unit pixels that are from the unit pixel 1100embodiment illustrated in FIG. 2.

Referring to FIG. 2, the unit pixel 1100 according to this embodimentmay receive a power supply voltage V_PIX and a row signal R_SIG and mayoutput the output signal COL_OUT. The image sensor 5 may include a rowdriver (not shown) that outputs the row signal R_SIG, and the unitpixels 1100 included in one row in the pixel array 1000 may receive thesame row signal R_SIG. The unit pixels 1100 included in one column, suchas column 1001 of FIG. 1, may share a line at which the output signalsCOL_OUT are respectively output by unit pixels 1100. Therefore, inresponse to the row signal R_SIG, the output signals COL_OUTrespectively corresponding to the unit pixels 1100 included in one rowmay be simultaneously output to the outside of the pixel array 1000 andtransmitted to the amplifier circuits 2000. In order to control aplurality of transistors included in the unit pixel 1100, the row signalR_SIG may be applied to gates of the transistors. The row signal R_SIGmay include a reset signal Rx, a transmission signal Tx, and a selectionsignal Sx. A voltage of the output signal COL_OUT may be determined inaccordance with the intensity of light sensed by the unit pixel 1100.

As illustrated in FIG. 2, the unit pixel 1100 may include a photodetecting device 1111, a transmission transistor 1121, a source-followertransistor 1122, a selection transistor 1123, and a reset transistor1124. In addition, the unit pixel 1100 may include a floating diffusionnode 1112 to which the transmission transistor 1121, the source-followertransistor 1122, and the reset transistor 1124 are electricallyconnected. The photo detecting device 1111 absorbs light andresponsively generates an electrical signal in accordance with theintensity of the light, and may be, for example, a photodiode, aphotogate, or a phototransistor. FIG. 2 illustrates an exampleembodiment in which the photo detecting device 1111 is a photodiode.However, the inventive concept is not limited thereto.

The transmission transistor 1121 may transmit charges accumulated by thephoto detecting device 1111 to the floating diffusion node 1112 or mayblock the charges in accordance with the transmission signal Tx. Forexample, while the photo detecting device 1111 absorbs the light toaccumulate charges, the transmission signal Tx having a voltage that mayturn off the transmission transistor 1121 may be applied to the gate ofthe transmission transistor 1121. In addition, when the light is blockedso that the photo detecting device 1111 stops absorbing the light, thetransmission signal Tx having a voltage that may turn on thetransmission transistor 1121 may be applied to the gate of thetransmission transistor 1121.

The source-follower transistor 1122 may amplify a voltage of thefloating diffusion node 1112, and the selection transistor 1123 mayselectively output the amplified voltage in accordance with theselection signal Sx. The reset transistor 1124 may also apply a pixelvoltage V_PIX to the floating diffusion node 1112 or may stop the pixelvoltage V_PIX from being applied to the floating diffusion node 1112 inaccordance with the reset signal Rx. When the reset transistor 1124applies a pixel voltage V_PIX to the floating diffusion node 1112, thevoltage of the floating diffusion node 1112 may be a reset voltage thatis close to the pixel voltage V_PIX. The pixel voltage V_PIX may be avoltage that is high enough to reset the floating diffusion node 1112.

Before the voltage of the photo detecting device 1111 is transmitted tothe floating diffusion node 1112, the floating diffusion node 1112 maybe reset by the turned on reset transistor 1124. The reset voltage ofthe floating diffusion node 1112 may be amplified by the source-followertransistor 1122 and may be output external to the unit pixel 1100 whenthe selection transistor 1123 is turned on. When the reset voltage ofthe floating diffusion node 1112 is completely output, the resettransistor 1124 is turned off and the transmission transistor 1121 isturned on so that a voltage in accordance with the charges accumulatedby the photo detecting device 1111 may be transmitted to the floatingdiffusion node 1112. Like the reset voltage of the floating diffusionnode 1112, the changed voltage of the floating diffusion node 1112 maybe output external to the unit pixel 1100 through the source-followertransistor 1122 and the selection transistor 1123.

The image sensor 5 may measure the intensity of the light absorbed bythe photo detecting device 1111 through a voltage difference between thereset voltage of the floating diffusion node 1112 and the voltagegenerated by the photo detecting device 1111. Such an operation isreferred to as correlated double sampling (CDS). An order in which theunit pixel 1100 outputs the reset voltage and the voltage generated bythe photo detecting device 1111 may vary. The image sensor 5 maycompensate for deviations among the unit pixels 1100 included in thepixel array 1000 through CDS.

The unit pixel 1100, including an element for amplifying the electricalsignal obtained by the photo detecting device 1111 absorbing the lightand converting the absorbed light, can be referred to as an active pixelsensor (APS). FIG. 2 illustrates an embodiment where the unit pixel 1100includes n-channel metal-oxide-semiconductor field-effect transistor(NMOS) transistors, which is only an example. The unit pixel 1100 mayinclude p-channel metal-oxide-semiconductor field-effect transistor(PMOS) transistors, in other embodiments, as other examples. The unitpixel 1100 according to aspects of the inventive concept may be appliedto an APS of another structure including the photo detecting device1111, as well as the APS of the structure illustrated in FIG. 2.

FIG. 3 is a view illustrating an embodiment of an operation of the unitpixel 1100, according to an aspects of the inventive concept. Asdescribed with reference to FIG. 2, the output signal COL_OUT generatedby the unit pixel 1100 may be a signal of which a voltage changes inaccordance with the intensity of the incident light. For example, theoutput signal COL_OUT may be a signal of which a voltage is reduced asthe intensity of the incident light increases. As illustrated in FIG. 3,the voltage of the output signal COL_OUT may be maintained as 1.3Vbefore the voltage thereof changes in accordance with the incidentlight. Referring to FIGS. 2 and 3, the electrical signal generated bythe light absorbed by the photo detecting device 1111 may pass throughthe transmission transistor 1121, the floating diffusion node 1112, thesource-follower transistor 1122, and the selection transistor 1123 andthe voltage of the output signal COL_OUT may be finally reduced.

As illustrated in FIG. 3, when the intensity of the light incident onthe unit pixel 1100 is small (that is, when the intensity of the lightabsorbed by the photo detecting device 1111 is small), the voltage ofthe output signal COL_OUT may be reduced by 0.3V to transit to 1.0V. Onthe other hand, when the intensity of the light incident on the unitpixel 1100 is large (that is, when the intensity of the light absorbedby the photo detecting device 1111 is large), the voltage of the outputsignal COL_OUT may be reduced by 1V to transit to 0.3V.

Referring to FIGS. 1 and 3, according to an embodiment, the firstamplifier 2100 may amplify the output signal COL_OUT to a value of 1.0Vto correspond to the intensity of the light with low intensity with alarge gain (for example, x3 to x16) to output the first amplified signalAMP1_OUT. On the other hand, the second amplifier 2200 having a largesecond input dynamic range may amplify the output signal COL_OUT to avalue of 0.3V to correspond to the intensity of the light with highintensity to output the second amplified signal AMP2_OUT. The controlsignal CON_SIG may determine whether the first amplifier 2100 or thesecond amplifier 2200 amplifies the output signal COL_OUT.

According to various embodiments of the inventive concept, the controlsignal CON_SIG may be generated within the image sensor 5 and may bereceived by one or more components or devices outside of the imagesensor 5. A photographing apparatus including the image sensor 5 maysense the brightness of a subject before photographing the subject. Forexample, when the photographing apparatus including the image sensor 5is a camera, before a user of the camera presses a photographing buttonto photograph the subject and to generate image data, the brightness ofthe subject may be sensed in advance by the pixel array 1000. Therefore,the photographing apparatus (or the image sensor 5) may obtaininformation on the brightness of the subject in advance to generate thecontrol signal CON_SIG in accordance with the brightness of the subject.

For example, sensing the brightness of the subject in advance, thephotographing apparatus (or the image sensor 5) may compare an averagevalue of the output signals COL_OUT output by the unit pixels 1100included in the pixel array 1000 or a value of the output signal COL_OUTgenerated by a unit pixel at a specific position (for example, aposition designated by the user) among the unit pixels 1100 included inthe pixel array 1000 with a predetermined reference value to generatethe control signal CON_SIG for selecting the first or second amplifier2100 or 2200 when the subject is photographed. The brightness of thesubject may be sensed in advance of acquiring image data by a controllerincluded in the image sensor 5 or a processor connected to the imagesensor 5.

FIG. 4 is a view schematically illustrating an embodiment of an imagesensor 5′ according to an aspect of the inventive concept. FIG. 5 is aview illustrating an embodiment of an operation of the image sensor 5′according to an aspect of the inventive concept. As illustrated in FIG.4, the image sensor 5′ may include a pixel array 1000 and an amplifiercircuit 2000′. Since the pixel array 1000 can be the same as thatdescribed with reference to FIG. 1, description thereof will not begiven here.

According to this embodiment, the amplifier circuit 2000′ may include afirst amplifier 2100′ and a second amplifier 2200′. As illustrated inFIG. 4, according to the current embodiment, the first amplifier 2100′and the second amplifier 2200′ may be differential amplifiers, eachhaving two input signals. In addition, the image sensor 5′ may include areference signal generator 500 configured to generate a reference signalREF_SIG. The reference signal REF_SIG generated by the reference signalgenerator 500 may be input to each of the first and second amplifiers2100′ and 2200′ together with the output signal COL_OUT output by thepixel array 1000. As illustrated in FIG. 4, the output signal COL_OUTand the reference signal REF_SIG may respectively pass throughcapacitors C1 and C2 and are both input to each of the first and secondamplifiers 2100′ and 2200′.

The first amplifier 2100′ may have a first input dynamic range and thesecond amplifier 2200′ may have a second input dynamic range that islarger than the first input dynamic range. According to this embodiment,as illustrated in the example of FIG. 4, when the first and secondamplifiers 2100′ and 2200′ are differential amplifiers, the firstamplifier 2100′ may have a first input common-mode range and the secondamplifier 2200′ may have a second input common-mode range that is largerthan the first input common-mode range. An input common-mode rangerefers to a voltage range of input signals that the differentialamplifier (for example, the first or second amplifier 2100′ or 2200′)may normally amplify. In the differential amplifier, the input dynamicrange may be represented as the input common-mode range.

As described above, the ADC may be used for converting the output signalCOL_OUT output from the pixel array 1000 into digital data. Variouskinds of ADCs are well known in the art, and may be used. According tothe embodiment of the inventive concept, the image sensor 5′ may includea ramp-comparative ADC, as an example. The ramp-comparative ADC maygenerate a reference signal and may measure a length of duration of thesignal which is generated by comparing an analog signal with thereference signal.

As illustrated in the embodiment of FIG. 5, the reference signalgenerator 500 may generate the reference signal REF_SIG, of which avoltage is reduced with a uniform slope. The first and second amplifiers2100′ and 2200′ that are the differential amplifiers may generate outputsignals (that is, first and second amplified signals AMP1_OUT andAMP2_OUT) that change at points in time when the reference signalREF_SIG and the output signal COL_OUT intersect. The image sensor 5′ mayinclude a counter, and the counter may count the first and secondamplified signals AMP1_OUT and AMP2_OUT generated by the first andsecond amplifiers 2100′ and 2200′ to measure a magnitude of the outputsignal COL_OUT.

As described with reference to the embodiment of FIG. 2, the amplifiercircuit 2000′ may receive in advance the output signal COL_OUTcorresponding to the reset voltage of the floating diffusion node 1112through CDS. As illustrated in FIG. 5, the reference signal generator500 may generate the reference signal REF_SIG of which a voltage isreduced with the uniform slope at a starting point of a period T1. Asthe voltage of the reference signal REF_SIG is reduced with the uniformslope, the reference signal REF_SIG intersects the output signal COL_OUTat an end point of the period T1. In other words, REF_SIG and COL_OUThave the same magnitude where they intersect at the end of period T1.Therefore, the first or second amplifier 2100′ or 2200′ that is adifferential amplifier may be configured and arranged to output thefirst or second amplified signal AMP1_OUT or AMP2_OUT, of which avoltage is reduced to be lower than a threshold value VAL at the endpoint of the period T1. The counter may measure a time from the startingpoint of the period T1 at which the voltage of the reference signalREF_SIG generated by the reference signal generator 500 starts to bereduced to the end point of the period T1 at which the voltage of thefirst or second amplified signal AMP1_OUT or AMP2_OUT is reduced to belower than the threshold value VAL to measure the voltage of the outputsignal COL_OUT.

After the amplifier circuit 2000′ amplifies the output signal COL_OUTcorresponding to the reset voltage of the floating diffusion node 1112,the amplifier circuit 2000′ may receive the output signal COL_OUTcorresponding to the voltage generated by the photo detecting device1111. As illustrated in FIG. 5, as with measuring the output signalCOL_OUT corresponding to the reset voltage of the floating diffusionnode 1112, the reference signal generator 500 may generate the referencesignal REF_SIG of which a voltage is reduced with a uniform slope from astarting point of a period T2. As the voltage of the reference signalREF_SIG is reduced with the uniform slope, the reference signal REF_SIGintersects the output signal COL_OUT at an end point of the period T2.In other words, REF_SIG and COL_OUT have the same magnitude where theyintersect at the end of period T2. Therefore, the first or secondamplifier 2100′ or 2200′ that is a differential amplifier may output thefirst or second amplified signal AMP1_OUT or AMP2_OUT of which a voltageis reduced to be lower than the threshold value VAL at the end point ofthe period T2. The counter may measure a time from the starting point ofthe period T2 at which the voltage of the reference signal REF_SIGgenerated by the reference signal generator 500 starts to be reduced tothe end point of the period T2 at which the voltage of the first orsecond amplified signal AMP1_OUT or AMP2_OUT is reduced to be lower thanthe threshold value VAL to measure the voltage of the output signalCOL_OUT. In accordance with CDS, the image sensor 5′ may obtain adifference of a value obtained by the counter measuring the period T1from a value obtained by the counter measuring the period T2 to measurethe intensity of the light.

In various embodiments, according to aspects of the inventive concept,the reference signal generator 500 can generate the reference signalREF_SIG with a slope that varies in accordance with the intensity of thelight in the period T2. That is, the reference signal generator 500 maygenerate the reference signal REF_SIG with a slope that varies inaccordance with which one is selected between the first amplifier 2100′and the second amplifier 2200′ in the period T2. For example, thereference signal generator 500 may receive the control signal CON_SIG.When the reference signal generator 500 receives the control signalCON_SIG corresponding to selection of the first amplifier 2100′, thereference signal generator 500 may generate the reference signal REF_SIGwith a lower slope (that is, a slope at which the voltage is more slowlyreduced) than that in the period T1. In addition, when the referencesignal generator 500 receives the control signal CON_SIG correspondingto selection of the second amplifier 2200′, the reference signalgenerator 500 may generate the reference signal REF_SIG with a slope(that is, a slope at which the voltage is more rapidly reduced) that ishigher than that used in the period T1.

According to the current embodiment, the output signal COL_OUT having alarge value (or amount of change) in accordance with the intensity ofthe light with high intensity is amplified by the second amplifier 2200′together with the reference signal REF_SIG with the higher slope so thatit is possible to prevent a width of the period T2 from significantlyincreasing. In addition, the output signal COL_OUT having a small value(or amount of change) in accordance with the intensity of the light withlow intensity is amplified by the first amplifier 2100′ together withthe reference signal REF_SIG with the lower slope so that resolution ofthe intensity of the light with low intensity may be improved.

FIG. 6 is a circuit diagram of an embodiment of the first amplifier2100′ of FIG. 4 according to an aspect of the inventive concept. Asillustrated in FIG. 6, the first amplifier 2100′ may be a differentialamplifier including three NMOS transistors and two PMOS transistors. Asignal BIAS applied to a gate of the NMOS transistor to which a groundvoltage is applied to a source thereof is maintained uniform so that theNMOS transistor may function as a current source. As described later,the signal BIAS may function as the control signal CON_SIG for stoppingpower consumption of the first amplifier 2100′. The two PMOS transistorsto which a power supply voltage V_AMP is applied to sources thereof ofthe first amplifier 2100′ may function as current mirrors. In addition,the two PMOS transistors may function as loads of the two NMOStransistors to which the reference signal REF_SIG and the output voltageCOL_OUT are respectively applied to gates thereof. The differentialamplifier illustrated in FIG. 6 has a simple structure and may obtain alarge gain.

Additionally, in the first amplifier 2100′ illustrated in FIG. 6, arange of an input voltage may be limited by the NMOS transistors and thePMOS transistors that operate in a saturation region. For example, asillustrated in FIG. 6, a minimum voltage of the reference signal REF_SIGmay be obtained by adding a drain-source voltage when the NMOStransistor, a gate of which the voltage BIAS is applied, is in thesaturation region and a gate-source voltage (higher than a thresholdvoltage) of the NMOS transistor, a gate of which the reference signalREF_SIG is applied, to the ground voltage. Referring to FIG. 3, sincethe voltage of the output signal COL_OUT may be reduced as the intensityof the light increases, the first amplifier 2100′ may not normallyamplify the output signal COL_OUT corresponding to the light with highintensity. As described later, the output signal COL_OUT correspondingto the light with high intensity may be amplified by the secondamplifier 2200′.

Referring to FIG. 4, in order to turn on or off the first amplifier2100′, the control signal CON_SIG may be provided. According to theembodiment illustrated in FIG. 6, the control signal CON_SIG may includea signal that may block the power supply voltage V_AMP of the firstamplifier 2100′ and the signal BIAS applied to the gate of the NMOStransistor that functions as the current source. For example, when avoltage of the signal BIAS becomes the ground voltage, a current pathfrom the power supply voltage V_AMP of the first amplifier 2100′ toground potential may be blocked so that the power consumption of thefirst amplifier 2100′ may be stopped (that is, the first amplifier 2100′may be turned off).

FIGS. 7A and 7B are circuit diagrams illustrating different embodimentsof the second amplifier 2200′ of FIG. 4 according to aspects of theinventive concept. The embodiments illustrated in FIGS. 7A and 7B areamplifiers having large input common-mode ranges, which may be referredto as PMOS/NMOS input folded cascade amplifiers. According to thisembodiment, the second amplifier 2200′ illustrated in FIGS. 7A and 7Bmay consume more power than, for example, the first amplifier 2100′illustrated in FIG. 6. Therefore, as illustrated in FIG. 4, the controlsignal CON_SIG for turning off the first amplifier 2100′ or the secondamplifier 2200′ may be provided in accordance with the intensity of thelight.

As illustrated in the embodiment of FIG. 7A, a second amplifier 2200′amay include seven NMOS transistors and seven PMOS transistors. Thereference signal REF_SIG and the output signal COL_OUT that are inputsignals of the second amplifier 2200′a may each be applied to each gateof a pair of NMOS transistors and each gate of a pair of PMOStransistors. Since the reference signal REF_SIG and the output signalCOL_OUT are applied to the gates of the pair of NMOS transistors (thatis, due to a folded structure of the pair of NMOS transistors), an inputcommon-mode range of the second amplifier 2200′a may extend in adirection of a power supply voltage V_AMP of the second amplifier2200′a. In addition, since the reference signal REF_SIG and the outputsignal COL_OUT are applied to the gates of the pair of PMOS transistors(that is, due to a folded structure of the pair of PMOS transistors),the input common-mode range of the second amplifier 2200′a may extend ina direction of a ground voltage.

Referring to FIG. 4, the control signal CON_SIG may be provided in orderto turn on or off the second amplifier 2200′a. According to theembodiment illustrated in FIG. 7A, the control signal CON_SIG mayinclude a signal that blocks the power supply voltage VAMP of the secondamplifier 2200′a and a signal NBIAS that functions as a current sourceand that is applied to gates of the NMOS transistors to which the groundvoltage are applied to sources thereof. For example, when the voltage ofthe signal BIAS becomes the ground voltage, a current path from thepower supply voltage V_AMP of the second amplifier 2200′a to a groundpotential may be blocked so that power consumption of the secondamplifier 2200′a may be stopped (that is, the second amplifier 2200′amay be turned off). The control signal CON_SIG may include a signalPBIAS that functions as a current source and that is applied to a gateof the PMOS transistor to which the power supply voltage V_AMP isapplied to a source thereof. When a voltage of the signal PBIAS becomesthe power supply voltage V_AMP, the second amplifier 2200′a may beturned off.

On the other hand, the control signal CON_SIG may include a signal PCASor a signal NCAS. For example, when a voltage of the signal PCAS becomesthe power supply voltage V_AMP, the PMOS transistors to which the signalPCAS is applied to gates thereof may be turned off so that the currentpath from the power supply voltage V_AMP of the second amplifier 2200′ato the ground potential may be blocked. In addition, when a voltage ofthe signal NCAS becomes the ground voltage, the NMOS transistors towhich the signal NCAS is applied to gates thereof may be turned off sothat the current path from the power supply voltage V_AMP of the secondamplifier 2200′a to the ground potential may be blocked.

FIG. 7B is a circuit diagram of another embodiment of the secondamplifier 2200′ of FIG. 4 according to an aspect of the inventiveconcept. Referring to FIG. 3, when the output signal COL_OUT generatedby the unit pixels 1100 of the pixel array 1000 is a signal having avoltage that is reduced as the intensity of the light increases, theinput common-mode range of the second amplifier 2200′ of FIG. 4 mayextend in the direction of the ground voltage. Therefore, as illustratedin FIG. 7B, a second amplifier 2200′b may have a simpler structure thanthat of the second amplifier 2200′a embodiment illustrated in FIG. 7A.

As illustrated in the embodiment of FIG. 7B, the second amplifier 2200′bmay include four NMOS transistors and five PMOS transistors. Thereference signal REF_SIG and the output signal COL_OUT that are inputsignals of the second amplifier 2200′b may be applied to gates of a pairof PMOS transistors. Since the reference signal REF_SIG and the outputsignal COL_OUT are applied to the gates of the pair of PMOS transistors(that is, due to a folded structure of the pair of PMOS transistors), aninput common-mode range of the second amplifier 2200′b may extend in adirection of a ground voltage.

Referring to FIG. 4, the control signal CON_SIG provided to turn on oroff the second amplifier 2200′b may include the signal PBIAS, the signalNBIAS, or the signal NCAS illustrated in FIG. 7B. As described abovewith reference to FIG. 7A, the voltage of the signal PBIAS becomes thepower supply voltage V_AMP or a voltage of the signal NCAS or the signalNBIAS becomes the ground voltage so that power consumption of the secondamplifier 2200′b may be stopped (that is, the second amplifier 2200′bmay be turned off).

FIGS. 8A and 8B are circuit diagrams of other embodiments of theamplifier circuit 2000′ of FIG. 4, according to aspects of the inventiveconcept. Amplifier circuits 2000′a and 2000′b illustrated in FIGS. 8Aand 8B may have structures in which the first amplifier 2100′ and thesecond amplifier 2200′ of FIG. 4 are combined according to embodimentsof the inventive concept. In FIGS. 8A and 8B, the circuits marked withthick lines may perform an operation corresponding to that of the firstamplifier 2100′ of FIG. 4 and the circuits marked with thin lines mayperform an operation corresponding to that of the second amplifier 2200′of FIG. 4. The control signal CON_SIG may be used to determine whichoperation the amplifier circuits 2000′a and 2000′b perform between theoperations corresponding to those of the first amplifier 2100′ and thesecond amplifier 2200′ of FIG. 4. According to the embodimentsillustrated in FIGS. 8A and 8B, the control signal CON_SIG of FIG. 4 mayinclude at least one of the signals applied to the gates of the PMOStransistors or the NMOS transistors. The control signal CON_SIG will bedescribed in detail later.

As illustrated in the embodiment of FIG. 8A, the amplifier circuit2000′a may include seven NMOS transistors and seven PMOS transistors.The reference signal REF_SIG and the output signal COL_OUT may beapplied to each of gates of a pair of NMOS transistors and gates of apair of PMOS transistors. When the light with low intensity is incidenton the pixel array 1000 so that the amplifier circuit 2000′a performsthe operation corresponding to that of the first amplifier 2100′ of FIG.4, the circuit marked with the thin line in FIG. 8A may not operate, ormay be turned off. That is, the amplifier circuit 2000′a may amplify thereference signal REF_SIG and the output signal COL_OUT to output thefirst amplified signal AMP1_OUT. For example, the control signal CON_SIGmay include the signal PCAS and the power supply voltage V_AMP isapplied to the signal PCAS so that the amplifier circuit 2000′a mayperform the operation corresponding to that of the first amplifier 2100′of FIG. 4. The control signal CON_SIG may include the signal NCAS or thesignal NBIAS and the ground voltage may be applied as the signal NCAS orthe signal NBIAS so that the amplifier circuit 2000′a may perform theoperation corresponding to that of the first amplifier 2100′ of FIG. 4.

On the other hand, when the light with high intensity is incident on thepixel array 1000 so that the amplifier circuit 2000′a performs theoperation corresponding to that of the second amplifier 2200′ of FIG. 4,the circuit marked with the thick line in FIG. 8A may not operate, ormay be turned off. That is, the amplifier circuit 2000′a may amplify thereference signal REF_SIG and the output signal COL_OUT to output thesecond amplified signal AMP2_OUT. For example, the control signalCON_SIG may include the signal NBIAS and the ground voltage may beapplied as the signal NBIAS so that the amplifier circuit 2000′a mayperform the operation corresponding to that of the second amplifier2200′ of FIG. 4.

FIG. 8B is a circuit diagram of an embodiment of the amplifier circuit2000′ of FIG. 4, according to an aspect of the inventive concept. Asillustrated in the embodiment of FIG. 8B, the amplifier circuit 2000′bmay include seven NMOS transistors and five PMOS transistors. Thereference signal REF_SIG and the output signal COL_OUT may be applied toeach of gates of a pair of NMOS transistors and gates of a pair of PMOStransistors. When the light with low intensity is incident on the pixelarray 1000 so that the amplifier circuit 2000′b performs the operationcorresponding to that of the first amplifier 2100′ of FIG. 4, thecircuit marked with the thin line in FIG. 8B may not operate, or may beturned off. That is, the amplifier circuit 2000′b may amplify thereference signal REF_SIG and the output signal COL_OUT to output thefirst amplified signal AMP1_OUT. For example, the control signal CON_SIGmay include the signal NCAS or the signal NBIAS and the ground voltagemay be applied as the signal NCAS or the signal NBIAS so that theamplifier circuit 2000′b may perform the operation corresponding to thatof the first amplifier 2100′ of FIG. 4.

On the other hand, when the light with high intensity is incident on thepixel array 1000 so that the amplifier circuit 2000′b performs theoperation corresponding to that of the second amplifier 2200′ of FIG. 4,the circuit marked with the thick line in FIG. 8B may not operate, ormay be turned off. That is, the amplifier circuit 2000′b may amplify thereference signal REF_SIG and the output signal COL_OUT to output thesecond amplified signal AMP2_OUT. For example, the control signalCON_SIG may include the signal NBIAS and the ground voltage may beapplied as the signal NBIAS so that the amplifier circuit 2000′b mayperform the operation corresponding to that of the second amplifier2200′ of FIG. 4.

FIG. 9 is a view illustrating an embodiment of a structure of the imagesensor 5′ according to an aspect of the inventive concept. The imagesensor 5′ may be manufactured by semiconductor processes, for example.With the development of semiconductor process technology, a feature sizethat refers to a minimum channel length of a transistor is reduced usingsuch processes. With the reduction in the feature size of thesemiconductor processes, a lower power supply voltage is supplied sothat power consumption of a semiconductor device may be reduced and moresemiconductor devices may be integrated. However, since the unit pixels1100 included in the pixel array 1000 of the image sensor 5′ include thephoto detecting device 1111 that absorbs light, there may be limitationsin reducing a size of the unit pixel 1100, such that a pixel array maynot lend itself to the same reduction in size or power reduction asother types of circuits.

As illustrated in the embodiment of FIG. 9, the pixel array 1000including the unit pixels 1100 may be implemented in a first chip 10having a large feature size and other circuits, such as the amplifiercircuit 2000′, a reference signal generator 5000, and a counter 700, maybe implemented in a second chip 20 having a small feature size. Theamplifier circuit 2000′ may include the first amplifier 2100′ and thesecond amplifier 2200′. The counter 700 may count the signals output bythe amplifier circuit 2000′. The amplifier circuit 2000′ and the counter700 may function as an ADC for outputting a digital signal based on theoutput signal COL_OUT and the reference signal REF_SIG that are analogsignals.

As illustrated in the embodiment of FIG. 9, the first chip 10 and thesecond chip 20 may be stacked, one above the other. In this embodiment,the first chip having the pixel array is stacked on the second chiphaving the amplifier circuit. As described above, the image sensor 5′,in which two or more chips are stacked, may be referred to as a stackedimage sensor. The image sensor 5′ may include interconnecting members 30in order to transmit the output signals COL_OUT output by the pixelarray 1000 of the first chip 10 to the amplifier circuit 2000′ of thesecond chip 20. The interconnecting member 30 may be formed of aconductive material and may include, for example, a through silicon via(TSV), a back via stack (BVS), and a copper-to-copper (C2C).

As illustrated in the embodiment of FIG. 9, the first chip 10 mayinclude one or more pads 11 in order to electrically connect theinterconnecting members 30 and the pixel array 1000. In addition, thesecond chip 20 may include one or more pads 21 in order to electricallyconnect the interconnecting members 30 and the amplifier circuit 2000′.A size (for example, about 4.5 μm×2.0 μm) of the pad 11 or 21 may belarger than that (for example, about 1 μm×1 μm) of a unit pixel 1100.When the number of electrical signals transmitted between the first chip10 and the second chip 20 increases, the number of interconnectingmembers 30 increases so that the number of pads 11 or 21 may increase.Increase in the number of pads 11 or 21 may increase a size of the imagesensor 5′.

A power supply voltage (for example, 2.8V) supplied to the first chip 10may be higher than that (for example, 1.8V) supplied to the second chip20. As described with reference to FIG. 2, the pixel voltage V_PIXsupplied to the unit pixels 1100 included in the pixel array 1000 of thefirst chip 10 may be high enough to reset the floating diffusion node1112. On the other hand, a power supply voltage (for example, the powersupply voltage V_AMP in FIGS. 6 to 8B) that is lower than that suppliedto the first chip 10 may be supplied to the amplifier circuit 2000′included in the second chip 20 in order to reduce power consumption.Therefore, the amplifier circuit 2000′ normally amplifying the outputsignal COL_OUT generated by the unit pixels 1100 may be required,wherein a lower power supply voltage is supplied to the amplifiercircuit 2000′, and a higher voltage is supplied to unit pixels 1100.

For example, when the output signals COL_OUT output by the pixel array1000 are attenuated by the first chip 10, a signal to noise ratio (SNR)of the output signal COL_OUT corresponding to the light with lowintensity may deteriorate. In another example, when the output signalsCOL_OUT are selectively attenuated in accordance with the intensity ofthe light incident on the pixel array 1000, in order to prevent thesecond chip 20 from being damaged due to a difference in power supplyvoltage between the first chip 10 and the second chip 20, a switchingtransistor for selectively attenuating the output signals COL_OUT may bearranged in the first chip 10. In the current example, twointerconnecting members 30 (that is, a signal that is not attenuated andan attenuated signal) may be required for one output signal COL_OUT sothat the number of interconnecting members 30 and the number of pads 11and 21 may increase.

As described above, according to various embodiments, since theamplifier circuit 2000′ included in the second chip 20 may receive theoutput signals COL_OUT output by the pixel array 1000 directly, forinstance without any attenuation, the amplifier circuit 2000′ mayamplify the directly received output signals COL_OUT. Therefore, it ispossible to improve the SNR of the output signal COL_OUT and to preventthe size of the image sensor 5′ from increasing. In addition, since thefirst amplifier 2100′ and the second amplifier 2200′ of the amplifiercircuit 2000′ are selectively turned on or off in accordance with theintensity of the light incident on the pixel array 1000, the powerconsumption of the image sensor 5′ may be reduced.

When a pitch between the pads 11 is no more than two times that betweenthe unit pixels 1100 in the first chip 10, the pads 11 may be arrangedas illustrated in FIG. 9. That is, two pads respectively correspondingto two adjacent columns of the pixel array 1000 may be arranged onfacing sides of the first chip 10.

On the other hand, according to the embodiment of the inventive concept,the first amplifier 2100′ and the second amplifier 2200′ of theamplifier circuit 2000′ may be arranged in the first chip 10. That is,unlike in the embodiment illustrated in FIG. 9, the amplifier circuit2000′ and the pixel array 1000 may be arranged in the first chip 10. Inthis case, in the first chip 10, the amplifier circuit 2000′ and thepixel array 1000 may be separately arranged to receive different powersupply voltages from the first chip 10. At this time, the signal outputby the first amplifier 2100′ or the second amplifier 2200′ may betransmitted from the first chip 10 to the second chip 20 through theinterconnecting members 30.

FIG. 10 is a view illustrating an embodiment of a system 3000 includingan embodiment of an image sensor according to aspects of the inventiveconcept. The system 3000 may be one of a computing system, a camerasystem, a scanner, a vehicle navigator, a video phone, a securitysystem, and a movement detecting system, or the like that require imagedata.

As illustrated in the embodiment of FIG. 10, the system 3000 may includea central processing unit (or processor) (CPU) 3100, a non-volatilememory 3200, an image sensor 3300, an input and output apparatus 3400,and random access memory (RAM) 3500. The CPU 3100 may communicate withthe non-volatile memory 3200, the image sensor 3300, the input andoutput apparatus 3400, and the RAM 3500 through a bus 3600. The imagesensor 3300 may be implemented on an independent semiconductor chip andmay be implemented by one semiconductor chip in combination with the CPU3100. Referring to FIG. 1, the image sensor 3300 included in the system3000 illustrated in FIG. 10 may include the pixel array 1000 and theamplifier circuit 2000 including the first and second amplifiers 2100and 2200, which are described above according to various embodimentsfalling within the scope of the inventive concept. The first amplifier2100 may have a larger gain than that of the second amplifier 2200 andthe second input common-mode range of the second amplifier 2200 may belarger than the first input common-mode range of the first amplifier2100. The image sensor 3300 may select one of the first amplifier 2100and the second amplifier 2200 in accordance with the intensity of thelight by using the control signal CON_SIG and may measure the outputsignals COL_OUT received from the pixel array 1000 through the outputsignal of the selected amplifier.

The CPU 3100 may control the system 3000 and may transmit data to orreceive data from other elements through the bus 3600. For example, theCPU 3100 may receive data generated by the image sensor 3300 accordingto the embodiment of the inventive concept. The non-volatile memory 3200that maintains stored data although power is blocked may store, forexample, data generated by the image sensor 3300 or data obtained byprocessing the generated data. The RAM 3500 may function as a datamemory of the CPU 3100 and may be a non-volatile memory. The input andoutput apparatus 3400 may receive a command from a user of the system3000 or may output an image and/or voice to the user.

FIG. 11 is a view illustrating an embodiment of an electronic system4000 including an image sensor 4040 and interfaces, according to aspectsof the inventive concept. Referring to the embodiment of FIG. 11, theelectronic system 4000 may be implemented by a digital camera or a dataprocessing apparatus capable of using or supporting a mobile industryprocessor interface (MIPI) that may include a digital camera, forexample, a mobile phone, a personal digital assistant (PDA), a portablemedia player (PMP), tablet, phablet, or a smartphone. The electronicsystem 4000 may include, but is not limited to, an application processor4010, the image sensor 4040, and a display 4050.

Referring to FIG. 1, the image sensor 4040 illustrated in FIG. 11 mayinclude the pixel array 1000 and the amplifier circuit 2000 includingthe first and second amplifiers 2100 and 2200, which are described aboveaccording to the embodiments of the inventive concept. The image sensor4040 may select one of the first amplifier 2100 and the second amplifier2200 in accordance with the intensity of the light by using the controlsignal CON_SIG and may measure the output signals COL_OUT received fromthe pixel array 1000 through the output signal of the selectedamplifier.

A camera serial interface (CSI) host 4012 implemented in the applicationprocessor 4010 may serially communicate with a CSI apparatus 4041 of theimage sensor 4040 through a CSI. At this time, for example, an opticaldeserializer may be implemented in the CSI host 4012 and an opticalserializer may be implemented in the CSI apparatus 4041.

A display serial interface (DSI) host 4011 implemented in theapplication processor 4010 may serially communicate with a DSI apparatus4051 of the display 4050 through a DSI. At this time, for example, anoptical serializer may be implemented in the DSI host 4011 and anoptical deserializer may be implemented in the DSI apparatus 4051.

The electronic system 4000 may further include a radio frequency (RF)chip 4060 capable of communicating with the application processor 4010.A PHY chip 4013, which is a physical layer communication chip, of theelectronic system 4000 and a PHY chip 4061 of the RF chip 4060 maytransmit or receive data in accordance with MIPI DigRF specifications.

The electronic system 4000 may further include, but is not limited to, aglobal positioning system (GPS) 4020, a storage unit 4070, dynamic RAM(DRAM) 4085, a speaker 4090, and a microphone 4080. The electronicsystem 4000 may perform communication by using a Wimax 4030, a wirelesslocal area network (WLAN) 4100, and/or an ultra-wideband (UWB) 4110.

While embodiments in accordance with the inventive concept have beenparticularly shown and described with reference to exemplary drawingsthereof, it will be understood that various changes in form and detailsmay be made therein without departing from the spirit and scope of thefollowing claims, which cover that shown and described with respect tothe figures, as well as physical and/or functional equivalents thereof.

What is claimed is:
 1. An image sensor comprising: a pixel arraycomprising a plurality of unit pixels configured to generate an outputsignal is response to incident light; a first amplifier having a firstinput dynamic range; and a second amplifier having a second inputdynamic range that is larger than the first input dynamic range, whereinone of the first and second amplifiers amplifies the output signal inaccordance with the intensity of light.
 2. The image sensor of claim 1,further comprising: a reference signal generator configured to generatea reference signal, wherein the first and second amplifiers aredifferential amplifiers configured to each receive the reference signaland the output signal as inputs and to measure the output signalrelative to the reference signal.
 3. The image sensor of claim 2,wherein the second amplifier is a complementarymetal-oxide-semiconductor (CMOS) input folded cascade amplifier.
 4. Theimage sensor of claim 1, wherein: the image sensor comprises stackedfirst and second chips, the pixel array is arranged in the first chip,and the first and second amplifiers are arranged in the second chip. 5.The image sensor of claim 4, wherein a feature size of the first chip islarger than that of the second chip.
 6. The image sensor of claim 4,wherein a power supply voltage of the first chip is higher than that ofthe second chip.
 7. The image sensor of claim 4, further comprising: atleast one interconnecting member coupled between the first chip and thesecond chip to transfer the output signal between the first and secondchips, wherein the interconnecting member is electrically connected tounit pixels corresponding to a column of the pixel array.
 8. The imagesensor of claim 4, further comprising: a counter configured to convert asignal amplified by the first or second amplifier into a digital signal,wherein the counter is arranged in the second chip.
 9. The image sensorof claim 1, wherein: the first and second amplifiers are configured toreceive a control signal, and a power consumption of the first amplifieror the second amplifier is stopped depending on a voltage level of thecontrol signal.
 10. An image sensor comprising: a first chip including apixel array comprising a plurality of unit pixels configured to generatean output signal in accordance with incident light; a second chipincluding first and second amplifiers with different input dynamicranges, such that one of the first and second amplifiers amplifies theoutput signal depending on the intensity of the incident light; and aninterconnecting member arranged to transmit the output signal from thefirst chip to the second chip, wherein the first and second chips arestacked.
 11. The image sensor of claim 10, wherein: a feature size ofthe first chip is larger than that of the second chip, and a powersupply voltage of the first chip is higher than that of the second chip.12. The image sensor of claim 10, wherein: an input dynamic range of thesecond amplifier is larger than that of the first amplifier, and a gainof the first amplifier is larger than that of the second amplifier. 13.The image sensor of claim 10, wherein: the second chip further comprisesa reference signal generator configured to generate a reference signalused to measure the output signal, and the first and second amplifiersare differential amplifiers that receive the reference signal and theoutput signal as inputs.
 14. The image sensor of claim 10, wherein: thefirst and second amplifiers receive a control signal, and powerconsumption of one of the first and second amplifiers is stopped inaccordance with the control signal.
 15. The image sensor of claim 10,wherein the interconnecting member is electrically connected to unitpixels corresponding to a column of the pixel array.
 16. An imagesensor, comprising: a pixel array comprising a plurality of unit pixelsconfigured to generate a plurality of output signals is response toincident light; and a plurality of amplifier circuits configured toreceive the plurality of output signals, each amplifier circuitcomprising: a first amplifier having a first input dynamic range andconfigured to amplify the output signal when the incident light has alow intensity; and a second amplifier having a second input dynamicrange that is larger than the first input dynamic range, and configuredto amplify the output signal when the incident light has a highintensity.
 17. The image sensor of claim 16, wherein the first amplifierhas a larger gain than the second amplifier.
 18. The image sensor ofclaim 16, wherein: the first and second amplifiers are configured toreceive a control signal, and a power consumption of the first amplifieror the second amplifier is stopped depending on a voltage level of thecontrol signal.
 19. The image sensor of claim 16, wherein: the pixelarray is formed on a first chip; and the plurality of amplifiers isformed on at least one second chip.
 20. The image sensor of claim 19,further comprising: an interconnecting member arranged to transmit theoutput signal from the first chip to the at least one second chip,wherein the first chip and the at least one second chip are stacked.